To reproduce:

1. Download attached project "TestSocket2018.3.zip" and open in Unity
2. Open "SampleScene" scene
3. Enter to Play mode
4. Observe that UI.Text GameObject and Console throws Error:

SocketException: Only one usage of each socket address (protocol/network address/port) is normally permitted.

5. Exit Play mode
6. Set Scripting Backend to IL2CPP and build Standalone Player
7. Launch Standalone Build

Expected results: Like in Unity Editor, Standalone also throws same Error
Actual results: Standalone Build does not throw any Errors

Notes:
- This issue only occurs in Windows Standalone
- On macOS Standalone, iOS and other Platforms everything works as expected
- On macOS Standalone and iOS I get different Error:

SocketException: Address already in use

Reproduced on Unity 2018.1.6f1, 2018.1.9f2, 2018.2.21f1, 2018.3.8f1, 2019.1.0b6 and 2019.2.0a7